Circuit switching is a WAN switching method in which a dedicated physical circuit is established, maintained, and terminated through a carrier network for each communication session. Circuit switching accommodates two types of transmissions: datagram transmissions and data-stream transmissions. Used extensively in telephone company networks, circuit switching operates much like a normal telephone call. Integrated Services Digital Network (ISDN) is an example of a circuit-switched WAN technology.

Packet Switching

Packet switching is a WAN switching method in which network devices share a single point-to-point link to transport packets from a source to a destination across a carrier network. Statistical multiplexing is used to enable devices to share these circuits. Asynchronous Transfer Mode (ATM), Frame Relay, Switched Multimegabit Data Service (SMDS), and X.25 are examples of packet-switched WAN technologies.

– Network devices share a point-to-point link to transport packets from a source to a destination across a carrier network

– Statistical multiplexing is used to enable devices to share these circuits

– Examples: ATM, Frame Relay, SMDS, X.25

WAN Virtual Circuits

– A logical circuit ensuring reliable communication between two devices

– Switched virtual circuits (SVCs)

– Dynamically established on demand – Torn down when transmission is complete – Used when data transmission is sporadic

– Permanent virtual circuits (PVCs)

– Permanently established – Save bandwidth for cases where certain virtual circuits must exist all the time

– Used in Frame Relay, X.25, and ATM

A virtual circuit is a logical circuit created to ensure reliable communication between two network devices. Two types of virtual circuits exist: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs). Virtual circuits are used in Frame Relay and X.25 and ATM.

SVCs are dynamically established on demand and are torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic.

PVCs are permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time.

WAN Protocols

The OSI model provides a conceptual framework for communication between computers, but the model itself is not a method of communication. Actual communication is made possible by using communication protocols. A protocol implements the functions of one or more of the OSI layers. A wide variety of communication protocols exist, but all tend to fall into one of the following groups:

– LAN protocols: operate at the physical and data link layers and define communication over the various LAN media

– WAN protocols: operate at the lowest three layers and define communication over the various wide-area media.

– Network protocols: are the various upper-layer protocols in a given protocol suite.

PPP:-Point-to-Point Protocol. Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits with built-in security features. Works with several network layer protocols, such as IP, IPX, & ARA.